Bascule bridge



Dec. 22, 1970 R. OVERSON BASCULE BRIDGE Filed June #3, 1968 FIG.2

3 Sheets-Sheet l INVENT OR REED OVERSON ATTORNEY Filed June 13. 1968 Dec. 22,1970 R. OVERSON 3,548,434

' I BASCULE BRIDGE 3 Sheets-Sheet a INVENTOR REED OVERSON ATTORNEY R. OVERSON BAscuLm 3mm Deb. 22, 1970 3 Sheets-Sheet 3 Filed June-13, 1968 CWT cwT- ll BRIDGE ONLY IOOO m m w m N O S R W O D E E R BRIDGE AND COUNTERWEIGHT RAISING LOWERING BRIDGE TIP VELOCITY ATIY United States Patent O 3,548,434 BASCULE BRIDGE Reed Overson, Walla Walla, Wash., assignor to the United States of America as represented by the Secretary of the Army Filed June 13, 1968, Ser. No. 736,628 Int. Cl. E01d 15/06 U.S. Cl. 1436 6 Claims ABSTRACT OF THE DISCLOSURE This invention comprises a bascule bridge mechanism wherein the bridge tail bracket is rotated about the trunnions by a force imparted by a crank arm through a connecting rod. The crank arm and an offset counterweight, which cooperate to reduce maximum crankshaft torque and control bridge tip velocity, are driven by a crankshaft powered by a conventional motor.

The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to me of any royalty thereon.

BACKGROUND OF THE INVENTION (1) Field of the invention The bascule bridge is a movable bridge that rotates in a vertical plane about a trunnion or trunnions. The plane or rotation is normally parallel to trafiic crossing the bridge in order to permit passage of other traflic through the position in which the bridge is ordinarily located.

(2) Description of the prior art The most significant problems arising in the bascule bridge art consist of limiting size and complexity of the counter-weight system and controlling rapid operation of the bridge. Many improvements inbascule bridges comprised of linkages between the bridge and the counterweight are attempts to deal with the foregoing problems. Some such mechanisms have included a moving pinion to engage a rack on an operating strut and a moving rack which engages a fixed pinion to provide the counterweight with a control mechanism for operation of a bascule bridge. In the Overhead counterweight type of mechanism an offset counterweight is linked to the bridge so that the bridge is continuously parallel to the arm supporting the counterweight. Although it has many intermoving parts, this type configuration is advantageous when there is insuificient space adjacent to the bridge structure for the counterweight.

While existing bascule bridges, including those described above, alleviate some of the design problems inherent in a bascule structure, other troublesome characteristics remain. Most existing bascule bridges require variable speed motors, positive bridge locks and large areas for bridge machinery. Moreover, existing bascule designs result in maximum acceleration and minimum control at the points where those characteristics are least desirable: the initial stages of opening and the final stages of closing.

SUMMARY OF THE INVENTION The present invention provides for a bascule bridge having an improved mechanical linkage which is comprised of a crankshaft operated by a conventional power source, a crank arm driven by the crankshaft, a counterweight fixedly attached to the crankshaft in a position designed to reduce maximum crankshaft torque and provide a locking force when the bridge is in an operating position and a connecting rod leading from the crank arm to the bridge tail. In its initial position the crank arm has a high mechanical advantage which augments the driving force applied to the bridge and the counterweight, both of which oppose initial movement.

It is an object of the present invention to provide means for operating a bascule bridge having a smaller counterweight for a given bridge mass and bridge tail length.

It is another object of the invention to provide a bascule bridge having no requirement for a bridge tail lock.

It is a further object of the invention to reduce the dimensions of the area required for the bridge operating mechanism.

It is still another object of the invention to reduce the amount of control equipment required for bridge operation through incorporation of accelerative and decelerative design characteristics.

It is a still further object of the invention to provide a bridge which is operable with a squirrel cage motor as a power source rather than a variable speed motor as conventionally used.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of the bascule bridge in the closed position including a cut-away view of the drive mechanism.

FIG. 2 is a side view of the bascule bridge in the open position with a cut-away view of the drive mechanism.

FIG. 2A is a side, cut-away view of the counterweight mechanism when the bridge is in a partly open position.

FIG. 3 is a motion diagram of the drive mechanism shown schematically in eighteen positions throughout its operational cycle.

FIG. 4 is a graphical representation of crank angle plotted against bridge tip velocity and crankshaft torque.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 of the drawing, reference numeral 1 depicts the power source which drives the horizontal crankshaft 2. At an angle from the horizontal and perpendicular to the crankshaft 2 is the counterweight 3 which is rigidly attached to the crankshaft 2 by a connecting means 8. Also, rigidly and perpendicularly attached to the crankshaft 2 is the linkage means 4, 5 between the crankshaft 2 and the bridge tail bracket 6, comprising a crank arm 4 rigidly attached to the crankshaft 2, and a connecting rod 5 hingedly attached at its ends to the distal end of the crank arm 4 and to the bridge tail bracket 6.

The power source 1, a squirrel cage motor as opposed to the variable speed motor that is conventionally required, imparts a clockwise rotary motion to the crankshaft 2 when the bridge begins to open. The motion of the crankshaft 2 imparts force on the bridge tail bracket 6 by the crank arm 4 through the connecting rod 5. AS rotation begins at the start of the lift process the counterweight 3 resists the effort of the drive mechanism, but he mechanical advantage of the crank arm 4 reduces the required force. As the lift progresses the counterweight 3 approaches a position CWT-4 vertically above its center of rotation 2 thereby exerting decreasing resistance to the driving torque. Similarly, the bridge exerts a constantly The action of the counterweight 3 between CWT-16 and CW118 provides a decelerating force at an appropriate time and stores energy to assist operation of the bridge during the closing cycle.

During the closing cycle, operation of the bridge and the drive machinery is reversed from the opening cycle. As the closing cycle begins, the counterweight 3 and the power source 1 cooperate to provide the accelerative force while the linkage system compels large tail bracket 6 displacements for small angular movements by the crank arm 4. The weight of the bridge opposes crankshaft 2 rotation until the center of gravity of the bridge passes vertically over the trunnions 9. The counterweight 3 provides a decreasing accelerative force as it rotates from CWT-18 to CWT-16, a decelerative force as it rotates from CWT-16 to CWT-4 which increases from CWT-l6 to CWT-10 and decreases from CWT-10 to CWT-4, and an accelerative force as the bridge rotates from CWT-4 to CWT-0. The accelerative force provided by the counterweight 3 as it rotates from CWT-4 to CWT- is not useful to the closing operation; however, once the closing is completed the position of the counterweight 3 becomes significant. When the bridge is in the down position the counterweight 3 imparts a large counterclockwise moment to the crankshaft 2; hence a sudden dynamic unloading, e.g., a truck leaving the bridge, will not result in the bridge rotating on its trunnions 9 as would a conventional bascule bridge having no positive locking device. Accordingly, the invention eliminates the requirement for a separate locking mechanism.

Referring now to FIGS. 2 and 3, as the closing cycle commences unit angular displacements, 18C, 17C, 16C by the crank arm 4 result in relatively small bridge tail 6 displacements 18CR, 17CR, 16CR which increase to a maximum at about position 13CR then decrease. As the bridge nears the closed position, the bridge tail 6 displacements 3CR, 2CR, lCR, become very small and becomes zero at zero CR for unit angular displacements of the crank arm 4. The result, as shown in FIG, 4, is a low to zero bridge tip velocity at each end of travel and a relatively high velocity through the mid portion of the travel. Thus, minimum opening and closing cycle time is achieved without requiring a variable speed motor or complex electronic control at point of closing.

In one actual design the counterweight was at an angle of fifteen degrees from the horizontal and perpendicular to the crankshaft. To achieve the desired results herein described in this design the counterweight was located angularly relative to the bridge deck so that the counterweight commenced to move in an are at a point sixty degrees before top dead center and halted at a point twenty degrees after bottom dead center as the bridge deck moved from a closed to an open position.

I claim:

1. A bascule bridge comprising, in combination:

(a) a rotatable bridge span;

(b) crankshaft means and means for providing rotation to said crankshaft;

(c) linkage means connecting said bridge span and said crankshaft means, said linkage means further comprising a link rigidly attached to said crankshaft means; and

(d) counterweight means rigidly attached to said crankshaft means, said counterweight means being angularly related to said rigidly attached link and being positioned so that when said span is being raised said 4 counterweight will decrease resistance to the driving torque.

'2. A bascule bridge as defined in claim 1 wherein said rigidly attached link is a crank arm and said linking means connecting said bridge span to said crankshaft means is comprised of said crank arm pivotally attached to connecting rod means.

3. A bascule bridge as defined in claim 2 wherein said counterweight means is comprised of an arm connected at one end to said crankshaft with a counterweight on the opposite end thereof.

4. A bascule bridge as defined in claim 3 wherein said connecting rod means is pivotally connected to said bridge span and said crank arm and said connecting rod means constitute a variable effective length between said crankshaft and said pivotal connection to said bridge span, said pivotal connection between said connecting rod means and said bridge span rotating from a proximately rearward position of said crankshaft to a distally forward position of said crankshaft as said bridge span opens.

5. A bascule bridge comprising, in combination:

(a) a bridge span including a tail bracket rotatable in a vertical plane;

(b) crankshaft means disposed transversely of said bridge span;

(c) drive means for said crankshaft including speed control means;

(d) trunnion means connected to said tail bracket rotatably mounting said bridge span;

(e) crank arm means connected to said crankshaft;

(f) connecting rod means pivotally connected to said crank arm at one end and to said bridge tail bracket at the other end;

(g) gear drive means interconnecting said crankshaft and said crank arm; and

(h) a counterweight radially secured to said crankshaft by a counterweight arm, said arm being angularly related to said crank arm and both being forwardly of said crankshaft when said span is in a down position with said counterweight arm being the most forwardly so when said span is being raised said counterweight will assist in increasing torque after it passes its vertical position as said crankshaft is rotated.

6. A bascule bridge comprising, in combination:

(a) a span rotatable on a fixed trunnion;

(b) a driven crankshaft rearwardly of said trunnion;

(c) an arm connected to said crankshaft with a counterweight on the end thereof;

((1) a crank arm fixed to said crankshaft;

(e) a connecting link pivotally connected between the end of said span rearwardly of said trunnion and the end of said crank arm;

(f) said counterweight arm being angularly related to said crank arm and both being forwardly of the drive shaft when the span is in a down position with the counterweight arm being the most forwardly so that when the span is being raised the counterweight will assist in increasing torque after it passes its vertical position as the crankshaft is rotated.

References Cited UNITED STATES PATENTS 1,302,302 4/1919 Brown l4-36 1,519,189 12/1924 Brown l436 1,680,821 8/1928 Strauss 14--36 JACOB L. NACKENOFF, Primary Examiner 

